Tire with sidewall rubber insert

ABSTRACT

A pneumatic tire has a sidewall rubber insert axially inward of at least one carcass ply. Such insert may, for example, be an apex extending radially outward from the bead core region of the tire into the tire sidewall. Alternatively, it may be positioned higher in the sidewall portion of the tire and away from the bead core. Such insert is a rubber composition containing a dispersion of an ultra high molecular weight polyethylene and a dispersion of a starch composite.

FIELD

This invention relates to a pneumatic tire having a rubber insert in itssidewall axially inward of at least one carcass ply. Such insert may be,for example, an apex in extending radially outward from a bead core of atire into its sidewall. Alternatively, the insert may be positionedhigher in the sidewall portion of the tire and away from the bead core.Such insert is a rubber composition containing a dispersion of an ultrahigh molecular weight polyethylene and a dispersion of a starchcomposite.

BACKGROUND

It is sometimes desired to provide a tire having a sidewall of arelatively high stiffness to enhance a tire's handling, for example itscornering stability, when mounted on a rigid rim as a part of a wheel ofa vehicle. For example, see U.S. Pat. Nos. 4,024,901 and 4,067,373.

Often, a resin is added to an apex portion of a tire sidewall to make itstiffer. However, addition of a resin for such purpose, while increasinghardness for the rubber composition, may also adversely affect therubber composition's other desirable properties such as, for example,its rebound and permanent set properties.

Another method of increasing hardness for a tire apex is to increase itsreinforcing filler content (e.g.: its carbon black content). However,increasing the carbon black content for such rubber composition, whileincreasing its hardness, may adversely affect physical properties suchas, for example, its hysteresis and, therefore, its heat build-upproperty and also may disadvantageously increase its stiffness softeningwith strain history property.

The stiffness softening property relates to a comparative difference(e.g.: a reduction) between a first force (MPa) needed for applicationof about a one percent shear strain at 100° C. to the rubber sample anda second force (MPa) needed for the same shear strain; wherein anintermediate and significantly greater shear strain (e.g.: about a 50percent shear strain) is applied to the sample with an accompanyingrelaxation of the sample to its original size after each of said firstand intermediate shear strain applications. If there is only a minimal,if any, decrease in the second force, then it may be said that there islittle, if any, stiffness softening of the cured rubber sample.

In practice, a low stiffness softening of the rubber composition for theinsert is desired.

In the description of this invention, a stiffness of a cured rubbercomposition is a characteristic similar to modulus in a sense that it ismeasured in terms of MPa and relates to a force required to obtain aprescribed strain, or elongation, of a rubber composition.

In practice, it is desired that a rubber composition for the insert havea relatively high stiffness, or modulus, at an elongation of 100percent. While of a somewhat lesser significance, it is also desiredthat it also have a relatively high modulus at a larger elongation of300 percent.

For this invention, variation in methodology of increasing stiffness fora tire sidewall insert is desired.

In particular, it is desired herein to provide a tire with a sidewallhaving an insert which has a relatively high hardness represented ashaving a Shore D hardness (23° C.) in a range of about 35 to about 50,yet also having a Hot Rebound value at 100° C. of about 65 to about 80in order to reduce heat generation in the rubber composition underworking conditions as a tire sidewall insert.

In practice, for the relatively hard rubber compositions for the insertof this invention, the hardness values may be desired to be recited interms of a Shore D hardness rather than a Shore A hardness.

Historically, a tire is a composite of numerous components each servinga specific and unique function and cooperatively functioning to producea desired tire performance. In one aspect, a tire carcass may containone or more reinforcing carcass plies. A carcass ply is typically acontinuous layer of rubber-coated parallel cords which extend from beadto bead and functions as a reinforcing element of the tire. The pliesare usually turned up around the bead, thereby locking the bead into thecarcass. Such carcass reinforcing plies are well known to those havingskill in such art.

In one aspect of the invention, a tire sidewall insert may be a tireapex. The term “apex” as used herein refers to a rubber wedge locatedprimarily in the lower sidewall region extending radially outward fromthe tire's bead core into the sidewall of the tire, usually between acarcass ply and its turn-up portion. An apex portion of a tire is wellknown to those skilled in such art.

BRIEF DESCRIPTION OF THE DRAWING

The tire sidewall insert may be described by way of example and withreference to the accompanying drawing in which:

FIG. 1 is a partial cross-sectional view of a tire with a first insertof a rubber composition in its sidewall region shown as an apex adjacentto a carcass ply and to a bead core and a second insert in its sidewallregion spaced apart from the bead core.

DISCLOSURE AND SUMMARY OF THE INVENTION

In accordance with this invention, a toroidally-shaped tire is providedwhich is comprised of two spaced-apart relatively inextensible beadcores, a circumferential tread designed to be ground-contacting,sidewalls extending from said bead cores to said tread and a carcass,which contains said bead cores and sidewalls, comprised of at least onecord reinforced ply supporting said tread and extending from bead coreto bead core; wherein an insert of a rubber composition isjuxtapositioned to at least one of said carcass plies in the sidewallregion of the tire characterized that said insert is a rubbercomposition comprised of, based upon 100 parts by weight ofelastomer(s);

(A) 100 phr at least one elastomer selected from homopolymers andcopolymers of conjugated diene composition is hydrocarbons having from 4to 6 carbon atoms and copolymers of conjugated hydrocarbons having from4 to 6 carbon atoms and styrene and alpha-methylstyrene, preferablystyrene;

(B) about 5 to about 50, alternatively about 15 to about 40, phr of aparticulate ultra high molecular weight polyethylene having a numberaverage molecular weight average in a range of about 4.5 to about 8,alternatively about 5 to 8, million and having a melting point accordingto ISO Method No. 306 in a range of about 130° C. to about 150° C.,dispersed within said rubber composition of said insert;

(C) about 5 to about 40, alternatively about 5 to about 30, phr of aparticulate starch/plasticizer composite dispersed within said rubbercomposition of said insert;

(D) about 10 to about 50 phr of at least one reinforcing filler selectedfrom carbon black, precipitated silica, aluminosilicate and modifiedcarbon black having silanol units on its surface dispersed within saidrubber composition of said insert;

(E) a coupling agent for said silica, aluminosilicate, modified carbonblack and starch composite, as the case may be, having a moiety reactivewith silanol units contained on the surface of the silica,aluminosilicate and said modified carbon black and hydroxyl unitscontained in said starch composite, as the case may be, and anothermoiety interactive with said elastomer(s);

wherein said starch is composed of amylose units and amylopectin unitsin a ratio of about 15/85 to about 35/65, alternatively about 20/80 toabout 30/70, and has a softening point in a range of about 180° C. toabout 220° C.; wherein said starch/plasticizer composite has a softeningpoint in a range of about 110° C. to about 170° C. and where theplasticizer is a polymeric plasticizer having a softening point of lessthan 160° C.; wherein said softening points are determined according toASTM No. D1228.

In further accordance with this invention, said insert rubbercomposition, in its sulfur-vulcanized state, has a Shore D hardnessvalue at 23° C. in a range of about 35 to about 50, a 100 percentmodulus at 23° C. in range of about 3 to about 9 MPa and a Hot Reboundvalue at 100° C. in a range of about 50 to about 85.

In additional accordance with this invention, said insert is an apexwherein said apex extends radially outward from said bead core into anassociated sidewall region of the tire. In practice, said apex may havesubstantially a shape of an entruncated crescent with its entruncatedportion juxtapositioned to a bead core.

Alternatively, said insert may be juxtapositioned to and axially inwardof a at least one carcass ply in the sidewall region of the tire andspaced apart from said bead core.

In practice, it has been observed that use of a starch/plasticizer incombination with the ultra high molecular weight polyethylene (UHMWPE)inclusions (micro dispersions) can be used to obtain a higher modulus ofthe rubber composition at intermediate strains (e.g.: 100 percentelongations) believed to be due, at least in part, to increasedelastomer/UHMWPE/starch composite interactions.

For the purposes of this invention, it is believed that a significantcontribution of micro inclusion, or dispersion, of the ultra highmolecular weight polyethylene (UHMWPE) is to promote a significantlyhigher modulus of the rubber composition at relatively large strains(e.g.: 100 percent elongation).

The benefit of such properties, namely the relatively high 100 percentmodulus values as well as desirable high hot rebound value, relativelyhigh Shore D hardness and low stiffness softening for the sidewallinsert and apex of this invention, is to provide a tire with one or moreof enhanced handling characteristics.

In practice, the said reinforcing filler may be comprised of, forexample, about 10 to about 50 phr of carbon black and about 20 to about30 phr of precipitated silica and/or aluminosilicate. Alternatively,such reinforcing filler may be comprised of, for example, (i) carbonblack alone, (ii) about 20 to about 30 phr of carbon black and about 10to about 60 phr of precipitated silica and/or aluminosilicate and about5 to about 20 phr of said starch composite, (iii) about 30 to about 50phr of carbon black and about 10 to about 30 phr of said starchcomposite or (iv) about 15 to about 30 phr of carbon black, about 20 toabout 40 phr of modified carbon black and about 5 to about 30 phr ofstarch composite.

It is to be appreciated that a coupling agent is to be typically used incombination with said precipitated silica, aluminosilicate, with saidmodified carbon black and with said starch composite to aid in couplingsuch fillers to the elastomer(s) and to, thus, enhance their elastomerreinforcing effect. Such couplers are those which have a moiety reactivewith the surface of the silica, aluminosilicate and modified carbonblack (e.g. with silanol groups on the surface thereof) or with surfaceof the starch composite (e.g. hydroxyl groups) and another moietyinteractive with the elastomer(s).

The philosophy of utilizing coupling agents for such purpose is wellknown to those having skill in such art.

For the starch composite, it is to be appreciated that starch haspreviously been suggested for use in rubber products, includingstarch/plasticizer composites. For example, see U.S. Pat. No. 5,762,639.

Starch by itself, typically has a softening point of about 200° C. orabove and is considered herein to have a somewhat limited use in manyrubber products, primarily because rubber compositions are normallyprocessed by preliminarily blending rubber with various ingredients attemperatures in a range of about 140° C. to about 170° C., usually atleast about 160° C., and sometimes up to 180° C. which is not a highenough temperature to cause the starch (with softening temperature of atleast about 200° C.) to effectively melt and efficiently blend with therubber composition. As a result, the starch particles tend to remain inindividual domains, or granules, within the rubber composition ratherthan as a more homogeneous blend.

Thus, it is considered herein that such softening point disadvantage hasrather severely limited the use of starch as a filler, particularly as areinforcing filler, for many rubber products.

It is considered herein that a development of a starch/plasticizercomposition, or compositions, with a softening point significantly lowerthan that of the starch alone, may allow the starch to be more easilymixed and processed in conventional elastomer processing equipment.

Starch is typically represented as a carbohydrate polymer havingrepeating units of amylose (anhydroglucopyranose units joined byglucosidic bonds) and amylopectin, a branched chain structure, as iswell known to those having skill in such art. Typically, starch iscomposed of about 25 percent amylose and about 75 percent amylopectin(The Condensed Chemical Dictionary, Ninth Edition (1977), revised by G.G. Hawley, published by Van Nostrand Reinhold Company, page 813). Starchcan be, reportedly, a reserve polysaccharide in plants such as, forexample, corn, potatoes, rice and wheat as typical commercial sources.

It is considered herein that use of a starch/plasticizer composition, orcompositions, with a softening point significantly lower than that ofthe starch alone, can allow the starch to be more easily mixed andprocessed in conventional elastomer processing equipment.

In the practice of this invention, the starch/plasticizer composite maybe desired to be used, for example, as a free flowing, dry powder or ina free flowing, dry pelletized form. In practice, it is desired that thesynthetic plasticizer itself is compatible with the starch and has asoftening point lower than the softening point of the starch so that itcauses the softening of the blend of the plasticizer and the starch tobe lower than that of the starch alone. This phenomenon of blends ofcompatible polymers of differing softening points having a softeningpoint lower than the highest softening point of the individualpolymer(s) in the blend is well known to those having skill in such art.

For the purposes of this invention, the plasticizer effect for thestarch/plasticizer composite, (meaning a softening point of thecomposite being lower than the softening point of the starch), can beobtained through use of a polymeric plasticizer such as, for example,poly(ethylenevinyl alcohol) with a softening point of less than 160° C.Other plasticizers and their mixtures are contemplated for use in thisinvention, provided that they have softening points of less than thesoftening point of the starch, and preferably less than 160° C., whichmight be, for example, one or more copolymers and hydrolyzed copolymersthereof selected from ethylene-vinyl acetate copolymers having a vinylacetate molar content of from about 5 to about 90, alternatively about20 to about 70, percent, ethylene-glycidal acrylate copolymers andethylene-maleic anhydride copolymers. As hereinbefore stated, hydrolyzedforms of copolymers are also contemplated. For example, thecorresponding ethylene-vinyl alcohol copolymers and ethylene-acetatevinyl alcohol terpolymers may be contemplated so long as they have asoftening point lower than that of the starch and preferably lower than160° C.

In general, the blending of the starch and plasticizer involves what areconsidered or believed herein to be relatively strong chemical and/orphysical interactions between the starch and the plasticizer.

In general, the starch/plasticizer composite has a desired starch toplasticizer weight ratio in a range of about 0.5/1 to about 4/1,alternatively about 1/1 to about 2/1, so long as the starch/plasticizercomposition has the required softening point range, and preferably, iscapable of being a free flowing, dry powder or extruded pellets, beforeit is mixed with the elastomer(s).

Representative examples of synthetic plasticizers are, for example,poly(ethylenevinyl alcohol), cellulose acetate and diesters of dibasicorganic acids, so long as they have a softening point sufficiently belowthe softening point of the starch with which they are being combined sothat the starch/plasticizer composite has the required softening pointrange.

Preferably, the synthetic plasticizer is selected from at least one ofpoly(ethylenevinyl alcohol) and cellulose acetate.

For example, the aforesaid poly(ethylenevinyl alcohol) might be preparedby polymerizing vinyl acetate to form a poly(vinylacetate) which is thenhydrolyzed (acid or base catalyzed) to form the poly(ethylenevinylalcohol). Such reaction of vinyl acetate and hydrolyzing of theresulting product is well known to those skilled in such art.

For example, vinylalcohol/ethylene (60/40 mole ratio) copolymers can beobtained in powder or pellet forms at different molecular weights andcrystallinities such as, for example, a molecular weight of about 11700with an average particle size of about 11.5 microns or a molecularweight (weight average) of about 60,000 with an average particlediameter of less than 50 microns. In an alternative, they can becompacted into pellets and then blended with starch at an elevatedtemperature above the melting point of the copolymer itself.

Various blends of starch and ethylenevinyl alcohol copolymers can thenbe prepared according to mixing procedures well known to those havingskill in such art. For example, a procedure might be utilized accordingto a recitation in the patent publication by Bastioli, Bellotti and DelTrediu entitled “A Polymer Composition Including Destructured Starch AnEthylene Copolymer”, U.S. Pat. No. 5,403,374.

Other plasticizers might be prepared, for example and so long as theyhave the appropriate Tg and starch compatibility requirements, byreacting one or more appropriate organic dibasic acids with aliphatic oraromatic diol(s) in a reaction which might sometimes be referred to asan “esterification condensation reaction”. Such esterification reactionsare well known to those skilled in such art.

In practice, elastomers for said insert may be selected from, forexample, cis 1,4-polyisoprene, cis 1,4-polybutadiene, styrene/butadienecopolymers, high vinyl polybutadiene containing from 35 to 90 percentvinyl 1,2-groups and isoprene/butadiene copolymers.

In practice, the present invention relates to a pneumatic tire.Pneumatic tire conventionally means a laminated mechanical device ofgenerally toroidal shape (usually an open torus) having beads and atread and made of rubber, chemicals, fabric and steel or othermaterials. When mounted on the wheel of a motor vehicle, the tirethrough its tread provides traction and contains the fluid that sustainsthe vehicle load. The present invention relates to both bias andradial-ply tires. Preferably, the present invention is a radial-plytire. “Radial-ply” tire means a belted or circumferentially-restrictedpneumatic tire in which the carcass ply cords which extend from bead tobead are laid at cord angles between 65° and 90° with respect to theequatorial plane of the tire.

For a further understanding of the invention, reference is made to theaccompanying drawing.

The accompanying drawing is a cross-sectional view of a portion of atire (1), including a portion of its carcass with included bead core(2), sidewall (3) and reinforcing carcass plies (4 and 5), together witha circumferential tread (6).

In particular, the pneumatic tire sidewall (3) contains two steel cordreinforced carcass plies (4 and 5) with a turn-up portion (5A) and aterminal end (5B).

“Steel cord” means one or more of the reinforcement elements, formed byone or more steel filaments/wires which may or may not be twisted orotherwise formed which may further include strands so formed whichstrands may or may not be also so formed, of which the carcass ply inthe tire is comprised.

An apex (7) is in the immediate proximity of the carcass ply turn-up(5A) including the area above the bead core (2) and is encased by thecarcass ply (5) and carcass ply turn-up.

In accordance with one aspect of this invention, a rubber tire isprovided having an apex (7) in the region of the carcass ply turn-up(5A) as well as a sidewall insert (8) spaced apart from the bead core(2); wherein said rubber in said apex (7) and sidewall insert (8) is theabove-described sulfur-cured rubber composition for this invention.

While the drawing depicts the presence of both the specified apex (7)and the sidewall insert (8), it is to be understood that the apex (7)and sidewall insert (8) may be used together in the same tire and eachmay be used individually in a tire construction.

For this invention, an essential component is the insert for thesidewall as a rubber composition which contains both the particulatedispersion of ultra high molecular weight polyethylene and starchcomposite.

Representative examples of such ultra high molecular weightpolyethylenes are those obtainable as, for example, various GUR gradessuch as, for example, GUR 4120 a trademark of Hoechst GmbH.

In general, the ultra high molecular weight polyethylene can beutilized, for example, as a powdery polyolefin.

It is readily understood by those having skill in the art that therubber compositions used for the insert for this invention, particularlyas an apex for a tire sidewall, compounded by methods generally known inthe rubber compounding art, such as mixing the varioussulfur-vulcanizable constituent rubbers with various commonly usedadditive materials such as, for example, curing aids, such as sulfur,activators, retarders and accelerators, processing additives, such asoils, resins including tackifying resins, particulate reinforcement ashereinbefore discussed, and plasticizers, fillers, pigments, fatty acid,zinc oxide, waxes, antioxidants and antiozonants and peptizing agents.As known to those skilled in the art, depending on the intended use ofthe sulfur-vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts unless otherwise prescribed herein.

Typical amounts of tackifier resins, if used, comprise 1 to 20 phr. Suchprocessing aids can include, for example, aromatic, napthenic, and/orparaffinic processing oils. Typical amounts of antioxidants compriseabout 1 to about 5 phr. Representative antioxidants may be, for example,diphenyl-p-phenylenediamine, polymerized1,2-dihydro-2,2,4-trimethylquinoline and others, such as, for example,those disclosed in The Vanderbilt Rubber Handbook (1990), pages 343-362.Typical amounts of antiozonants comprise about 1 to about 5 phr.Representative antiozonants may be, for example, those disclosed in TheVanderbilt Rubber Handbook (1990), pages 363-367. Typical amounts offatty acids, if used, which can include stearic acid comprise about 0.5to about 3 phr. Typical amounts of zinc oxide comprise about 2 to about10 phr. Typical amounts of waxes comprise about 1 to about 5 phr. Oftenmicrocrystalline waxes are used. Typical amounts of peptizers compriseabout 0.1 to about 1 phr. Typical peptizers may be, for example,pentachlorothiophenol and dibenzamidodiphenyl disulfide. The presenceand relative amounts of the above additives are considered to be not anaspect of the present invention, unless otherwise provided herein, whichis more primarily directed to the utilization of the combination of adispersion of particulate ultra high molecular weight polyethylene andstarch composite in the rubber composition for the sidewall insert ofthis invention.

The vulcanization is conducted in the presence of a sulfur-vulcanizingagent. Examples of suitable sulfur-vulcanizing agents include elementalsulfur (free sulfur) or sulfur donating vulcanizing agents, for example,an amine disulfide, polymeric polysulfide or sulfur olefin adducts.Usually, the sulfur-vulcanizing agent is elemental sulfur. As known tothose skilled in the art, sulfur-vulcanizing agents are used in anamount ranging from about 1.5 to about 4 phr, alternatively about 2 toabout 4 phr or, even in some circumstances, up to about 8 phr. For ahigher modulus for the rubber composition, sulfur in an amount of about4 to about 6 phr might be used.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. Conventionally, a primary accelerator is used in amountsranging from about 0.5 to about 2.0 phr. In another embodiment,combinations of two or more accelerators which is generally used in thelarger amount (0.5 to 1.0 phr), and a secondary accelerator which isgenerally used in smaller amounts (0.05 to 0.50 phr) in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators have been known to produce a synergistic effect ofthe final properties and are somewhat better than those produced by useof either accelerator alone. In addition, delayed action acceleratorsmay be used which are not affected by normal processing temperatures butproduce satisfactory cures at ordinary vulcanization temperatures.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. Preferably, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator is preferably a guanidine, dithiocarbamate orthiuram compound.

The tire can be built, shaped, molded and cured by various methods whichwill be readily apparent to those having skill in such art.

The prepared tire of this invention is conventionally shaped and curedby methods known to those having skill in such art.

The invention may be better understood by reference to the followingexamples in which the parts and percentages are by weight unlessotherwise indicated.

EXAMPLE I

Rubber compositions are prepared which contain the materials shown inTable 1 which recite a Control rubber composition as Sample A as well asexperimental rubber compositions as Samples B, C and D which contain,variously, a dispersion of a particulate ultra high molecular weightpolyethylene (UHMWPE) and starch composite.

Ingredients, other than sulfur and accelerator(s), are mixed insequential two non-productive mixing stages to a temperature of about170° C. for about 5 minutes for each stage in an internal rubber mixer.All of the non-productive ingredients were introduced in the firstnon-productive mixing stage, or operation. The term “non-productive”means without sulfur curatives and is a term well known to those skilledin such art.

Sulfur and cure accelerator(s) were then mixed in a subsequent mixstage, often referred to as a “productive” mixing stage, in an internalrubber mixer for about 2 minutes to a temperature of about 115° C.

Table 2 reports the cure behavior and vulcanizate properties for theControl Sample A and also Samples B, C and D.

TABLE 1 Sample A Sample Sample Sample Material (Control) B C DNon-Productive Mixing (phr) Natural rubber¹ 100 100 100 100 Couplingagent² 0 0 5 0 UHMWPE³ 0 40 40 0 Starch composite⁴ 0 0 10 0 Carbon black40 40 40 75 (N630) Zinc oxide 6 6 6 6 Stearic acid 1.5 1.5 2 2 Resin(s)⁵0 0 0 20 Productive Mixing (phr) Sulfur 5 5 5 3.8 Accelerator(s)⁶ 0.70.7 5.5 5.5 ¹Natural cis 1,4-polyisoprene rubber. ²Coupling agentobtained as X50S, a trademark of Degussa AG as a 50/50 composite ofbis(3-triethoxysilylpropyl) tetrasulfide and carbon black, therefore,the amount of actual coupling agent is 2.5 phr. ³Ultra high molecularweight polyethylene having a molecular weight of about five millionobtained as GVR 4120 a trademark of the Hoechst GmbH company. ⁴Astarch/plasticizer composite obtained as Mater-Bi 1128RR a trademark ofthe Novamont company and understood to be a composite of starch andethylene/vinyl alcohol plasticizer. ⁵The resin(s) of theresorcinol/formaldehyde type. ⁶Vulcanization accelerators have beenadded and slightly adjusted for the different formulations.

The accelerator for Samples A and B was a butyl benzothiazole, and forSamples C and D, the accelerators used are dicyclohexyl benzothiazoleand hexamethylene type.

TABLE 2 A Property (Control) B C D Properties Modulus (100%), MPa 2.3 69.3 7 Modulus (300%), MPa 12.0 16.3 — — Shore A hardness 60 75 — — ShoreD hardness — — 42 42 Permanent 29 26 28 36 compression set (%) Rebound(100° C.) 83 80 67 53 Elongation @ Break 472 381 210 200 (%) TensileStrength 21.3 16.4 15 15 (MPa) Mooney viscosity 37 36 42 44 SpecificGravity 1.11 1.07 1.09 1.19 Stiffness 0 −5 −19 −36 softening (%)

It is readily seen from Table 2 that the intermediate modulus (100percent), as well as the 5 larger modulus (300 percent), is readilyenhanced by the presence of the micro-inclusion (dispersion) of theUHMWPE as shown by Sample B.

It is also seen that the intermediate modulus (100 percent) is furtherreadily enhanced by the micro-inclusion (dispersion) of both the UHMWPEand the starch composite as shown by Sample C.

Further, the hardness of the rubber composition is enhanced bymicro-inclusion (dispersion) of the UHMWPE and starch composite as shownby Samples B and C.

The stiffness softening was substantially reduced by the micro-inclusion(dispersion) of both the UHMWPE and the starch composite as shown bySample C.

Further, the Shore A and Shore D hardness compared to Rebound valuesshown in Table 2 illustrate that addition of the ultra high molecularweight polyethylene and starch composite can provide stiff rubbercompositions (hardness) values with a reduced hysteresis (Rebound) valuewhich are considered herein to be desirable for the sidewall insert.

The specific gravity property shown in Table 2 illustrates that use ofthe ultra high molecular weight polyethylene can also be used to reducethe weight of the rubber composition.

It may be pointed out that a combination of the starch compositedispersion and relatively high sulfur content for Sample C was used toachieve the higher 300 percent Modulus shown in Table 2.

It is considered herein that the use of the combination of starchcomposite and relatively high sulfur content enabled internal stressescreated by the hard inclusions of the ultra high molecular weightpolyethylene to be better distributed within the rubber composition and,thereby, reduce interfacial interactions at large strains (largeelongations) while maintaining sufficient tensile and elongationproperties.

The stiffness softening test may be conducted, for example, as describedas first determining an initial one percent shear modulus (MPa) at 100°C. After allowing the sample to relax to its original shape, the rubbersample is then stretched 50 percent in shear. After allowing the sampleto relax to its original shape, a second one percent shear modulus isdetermined for the rubber sample. If the second one percent shearmodulus for the rubber sample is substantially equal to the firstdetermined one percent shear modulus, then the sample has a very little,if any, softening with strain history or stiffness softening. On theother hand, if the second determined shear modulus is substantially lessthan the value of the first determined shear modulus, then the rubbersample may be said to have its softening with strain history negativelyof “adversely affected”.

In Table 2, the stiffness softening values are reported as percentdifferences between the first shear modulus value and the second shearvalue as above-referenced.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

What is claimed is:
 1. A toroidally-shaped pneumatic tire comprised oftwo spaced apart, relatively inextensible bead cores, a circumferentialtread designed to be ground-contacting, sidewalls extending from saidbead cores to said tread and a carcass which contains said tread andsidewalls, said carcass is comprised of at least one cord reinforcedrubber ply extending from bead core to bead core; wherein an insert of arubber composition is juxtapositioned to at least one of said carcassplies in each sidewall region of the tire; characterized in that saidinsert is a rubber composition comprised of, based upon 100 phr ofelastomer(s), A) at least one elastomer selected from homopolymers andcopolymers of conjugated diene hydrocarbons having from 4 to 6 carbonatoms and copolymers of conjugated diene hydrocarbons having from 4 to 6carbon atoms and styrene, (B) about 5 to about 50 phr of a particulateultra high molecular weight polyethylene having a weight averagemolecular weight in a range of about 4.5 million to about 8 million witha melting point in a range of about 130° C. to about 150° C. dispersedwithin said rubber composition of said insert, (C) from about 5 to about40 phr of a particulate starch/plasticizer composite dispersed withinsaid rubber composition of said insert, and (D) about 10 to about 50 phrof reinforcing filler comprised of carbon black and precipitated silica,and (E) a coupling agent for said silica and starch composite having amoiety reactive with silanol units contained on the surface of thesilica and hydroxyl units contained in said starch composite and anothermoiety interactive with said elastomer(s); wherein said starch iscomposed of amylose units and amylopectin units in a ratio of about15/85 to about 35/65, and has a softening point in a range of about 180°C. to about 220° C.; wherein said starch/plasticizer composite has asoftening point in a range of about 110° C. to about 170° C., and wherethe plasticizer is a polymeric plasticizer having a softening point ofless than 160° C.